Physical vapor deposition of titanium nitride on a nonconductive substrate

ABSTRACT

A process for physical vapor deposition of a refractory coating such as titanium nitride on a nonconductive substrate such as a ceramic substrate and the coated substrate produced thereby. The nonconductive substrate is coated by cleaning the nonconductive substrate surfaces and then depositing a first layer of a refractory metal such as titanium metal on the nonconductive substrate by physical vapor deposition. A second layer of a refractory compound such as titanium nitride is then deposited on the first layer by physical vapor deposition to produce a coated nonconductive substrate having enhanced coating adhesion.

This is a continuation of copending application Ser. No. 07/490,856filed on Mar. 9, 1990, now abandoned.

FIELD OF THE INVENTION

This invention relates to a process for physical vapor deposition of arefractory coating on a nonconductive substrate and the product producedthereby. More particularly, this invention relates to a process forphysical vapor deposition of a titanium nitride coating on a ceramicsubstrate and the product produced thereby.

DESCRIPTION OF THE RELATED ART

Various methods of physically depositing a vaporized material on asubstrate, such as a base metal, are well known. For example, a gaseousspecie may be physically deposited on a metal substrate by evaporation,reactive evaporation, ion-plating, and sputtering.

A typical ion-plating system for coating a substrate is described inU.S. Pat. No. 3,329,601. The system includes a vacuum chamber containinga metal source, an electron source such as a filament and a substratematerial supported within a substrate holder biased negatively withrespect to a plasma to be generated within the chamber. In operation,the chamber is evacuated and then filled with an inert gaseous specie,such as argon. Electrons are then emitted by the filament and the metalsource. Some of the electrons collide with neutral molecules in theplasma causing excitement and partial ionization of the gaseous species.This state of partially ionized and excited gaseous species along withfree electrons is generally referred to as the plasma. The excitedparticles, upon returning to lower energy states, also emit photons anda visible glow is observed surrounding the substrate. Under theinfluence of an applied electric field, argon ions from the "glow"region are accelerated and collide with the biased substrate,effectively cleaning the substrate surface of contaminants and raisingthe surface temperature of the substrate. Independent heating of thesubstrate may also be possible prior to ion bombardment. Once thecleaning is completed, a coating metallic source, such as titanium,contained within a crucible is heated by known means causing evaporationof the coating material into the glow discharge. The ionized metal isallowed to react with a gaseous specie such as ionized nitrogen duringthe ion-plating process. The ion-plating process results in a uniformcoating of a material such as titanium nitride, on the substrate.

Titanium and/or titanium nitride coatings have been successfully appliedby physical vapor deposition to cemented carbides and tool steelsubstrates. Illustrative of various processes for physical vapordeposition of a coating on a cutting tool are U.S. Pat. Nos. 4,469,489;4,406,669; 4,539,251 and 4,337,300.

However, because ceramic substrates are inherently electricallyinsulating, ion-plating of a titanium nitride coating on a ceramicsubstrate tends to build up an electrical charge on the substratesurface. The applied bias voltage between the plasma and the ceramicsubstrate influences the adhesive qualities of the titanium nitridecoating. Ineffective voltage biasing due to electrical charge buildupresults in flaking of the coating from the ceramic substrate therebyproducing a less than satisfactory coated ceramic.

To overcome the aforementioned problems, we have invented a novelprocess for physical vapor deposition of a refractory coating on anonconductive substrate. More particularly, the present inventionutilizes the ion-plating physical vapor deposition process for coatingwith titanium nitride any suitable nonconductive substrate such as asubstrate made of a ceramic material and the like. Any suitable ceramicsubstrate such as a sialon (Si-Al-ON) based ceramic substrate or Si₃ N₄based ceramic substrate or Al₂ O₃ based ceramic substrate including Al₂O₃ composites alloyed with or without additions of zirconia and/or otherhard materials such as Silicon Carbide whiskers may be coated by thepresent invention. The present invention provides a process fordepositing a titanium nitride coating on the nonconductive substrate byovercoming the ineffectiveness of the applied bias voltage between theplasma and the insulating substrate.

Accordingly, an object of the present invention is to provide a coatingwith an improved adhesion strength to a tool or article by a physicalvapor deposition process, such as ion-plating.

Another object of the present invention is to provide a coated articleor tool having high wear resistance, heat resistance and corrosionresistance.

Yet another object of the present invention is to provide cutting tools,wear resisting tools, wear parts and decorative articles with animproved wear resistance, heat resistance and corrosion resistance.

SUMMARY OF THE INVENTION

Briefly, according to this invention, there is provided a process ofphysical vapor deposition of a refractory coating, preferably a titaniumnitride coating on a nonconductive substrate such as a ceramicsubstrate. The process involves cleaning the nonconductive substratesurfaces and then depositing by physical vapor deposition a first layerof a refractory metal such as titanium and then depositing a secondlayer of a refractory metal compound such as titanium nitride to producea coated nonconductive substrate having enhanced coating adhesion.

The first layer increases the electrical conductivity of thenonconductive substrate such that electrical biasing in the ion-platingprocess becomes effective. An ion-plated titanium nitride coating on aceramic substrate, such as a ceramic insert cutting tool, has been foundto reduce flank wear, reduce the coefficient of friction between thecutting tool and a workpiece such as cast iron or nickel-basedsuperalloy in the instance of Si-Al-ON based ceramic substrates orcarbon and high temperature steels in the instance of Al₂ O₃ basedceramic substrates, resulting in reduced frictional forces, and becauseof the chemical stability of titanium nitride, act as a diffusionbarrier between the insert cutting tool and the workpiece therebyreducing tool cratering, flank wear and notching problems.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and other objects and advantages of this invention willbecome clear from the following detailed description made with referenceto the drawings in which:

FIG. 1 is a perspective view of a Kenloc style insert; and

FIG. 2 is a perspective view of a Kendex style insert.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the present invention is described in reference to anion-plating physical vapor deposition process for coating anonconductive ceramic substrate, the present invention may also be usedto coat most any suitable nonconductive substrate. The nonconductivesubstrate is coated by cleaning the nonconductive substrate surface andthen depositing a first layer of titanium on the cleaned substratesurface. A second layer of titanium nitride is then deposited upon thefirst layer to produce a coated substrate having an outer layer coatingexhibiting enhanced adhesion properties.

In an ion-plating physical vapor deposition process, the nonconductivesubstrate acts as an electrical insulator as opposed to beingelectrically conductive, thereby causing an electrical charge to buildup on the substrate surface. The buildup of the electrical chargeeffectively decreases the applied bias on the substrate, which in turnresults in a poor adhesive quality of a titanium nitride coating to anonconductive substrate.

It will be appreciated that the physical vapor deposition process of thepresent invention may also include evaporation, reactive evaporation,ion-plating, sputtering, and magnetron sputtering and is not limited toion-plating. However, in a preferred embodiment, the titanium nitridelayer is deposited by ion-plating wherein the material to be vapordeposited is energized as positive ions by applying a negativeaccelerating voltage to the substrate. As used herein, ion-plating isthe process occurring at the substrate and is effectively independent ofthe method used to generate the ions which combine to form the coatingcompound. For example, a variety of methods to produce metallic ions maybe used for ion plating, such as thermal evaporative ion-plating,sputter ion-plating or arc evaporative ion-plating and the like.

The present invention is applicable in the production of a coatedarticle such as a cutting tool insert having a nonconductive ceramicinsert substrate. The cutting tool insert may be made by conventionalceramic powder processing techniques and densified by either hotpressing or pressureless sintering. The ceramic insert substrate mayinclude Si-Al-ON based ceramic cutting inserts, Al₂ O₃ based ceramiccutting inserts and other articles such as but not limited to thatmarketed by Kennametal Inc. under the designations KYON 2000, KYON 3000and K090. KYON and K090 are registered trademarks of Kennametal Inc. forceramic materials and wear resisting pieces in the form of cutting toolinserts and for wear resisting pieces consisting of hard ceramicmaterial in the form of cutting tool inserts-namely, inserts for use indies and tools for cutting, shaping or forming materials; respectively.

The Si-Al-ON grade cutting inserts may be either beta-prime Si-Al-ON,alpha-prime Si-Al-ON, or mixtures thereof, and may also contain a glassyphase ranging from zero to 10 percent by weight. Kyon 3000 is abeta-prime Si-Al-ON expressed by the chemical formula Si_(6-z) Al_(z)O_(z) N_(8-z) wherein z has a value greater than 0 but less than 4.2.For a description of a beta-prime Si-Al-ON material reference is made toU.S. Pat. No. 4,127,416, which is incorporated herein by reference. KYON2000 is an alpha-prime beta-prime Si-Al-ON. Alpha-prime Si-Al-ON isexpressed by the chemical formula M_(x) (Si,Al)₁₂ (O,N)₁₆ wherein x islarger than 0 but not more than 2 and M is at least one selected fromthe group consisting of Li, Na, Ca, Mg, Y, and any rare earth element.For a complete description of mixed alpha-prime beta-prime Si-Al-ONcompositions useful for cutting tool inserts, reference is made to U.S.Pat. Nos. 4,563,433 and 4,547,470, which are incorporated herein byreference.

Among the various Al₂ O₃ based ceramic cutting inserts contemplated bythe present invention are cutting inserts having an Al₂ O₃microstructure in which SiC and/or refractory metal (titanium, hafnium,vanadium, tantalum, zirconium, and niobium) compounds (oxides, nitrides,carbides and carbonitrides) such as preferably TiC and/ or ZrO₂particles and/or SiC or TiC whiskers dispersed therein. As disclosed inMehrotra et al. U.S. Pat. No. 4,959,332 assigned to Kennametal Inc., thealumina based ceramic cutting inserts may be provided with about 1.5 to12.5 v/o (volume percent) silicon carbide whiskers and about 7.5 to 17.5v/o zirconia dispersed in an alumina based matrix. Yet another Al₂ O₃based ceramic cutting insert is described in Mehrotra et al. U.S. Pat.Nos. 4,959,331 and 4,965,231 and assigned to Kennametal Inc., the Al₂ O₃based cutting inserts may contain about 1.5 to 17.5 v/o silicon carbidewhiskers, about 5 to 17.5 v/o zirconia, the residue of a magnesium oxideor other magnesium-oxygen compound addition, and at least 4 v/otetragonal zirconia. Still another Al₂ O₃ based cutting insert isdescribed in Mehrotra et al. U.S. Pat. No. 4,960,735 assigned toKennametal Inc. The Al₂ O₃ based cutting insert described in U.S. Pat.No. 4,960,735 may include 1.5 to 37.5 v/o silicon carbide whiskers,about 5 to 17.5 v/o zirconia, the residue of a magnesium oxide or othermagnesium-oxygen compound addition, and at least 2 v/o tetragonalzirconia. Silicon carbide whiskers (SiC_(w)) are discontinuous, singlecrystal Silicon carbide (SiC) fibers and are well known in the art. Thesilicon carbide whiskers utilized may be of any commercially availablebrand which have been used in the past in the alumina based cuttinginserts. It will be appreciated that a layer of TiN over a Al₂ O₃ -SiCwhisker reinforced composite may provide a chemically inert barrier toprevent reaction of the SiC whiskers with a steel workpiece.

For an example of a ceramic composition including an alumina matrixhaving titanium carbide (TiC) whiskers dispersed therein reference ismade to U.S. Pat. No. 4,852,999 assigned to Kennametal Inc.

U.S. Pat. No. 4,852,999 and U.S. Pat. Nos. 4,959,332; 4,959,331;4,965,234 and 4,960,735 assigned to Kennametal Inc. are incorporatedherein by reference.

A preferred composition of an Al₂ O₃ based ceramic insert may containabout 5-10 v/o zirconia with or without sintering aid additions,particles and/or whiskers of refractory metal compounds and/or SiCwhiskers.

The Al₂ O₃ based ceramic inserts are prepared by grinding the insertsurfaces to a fine finish. A die penetrant of a type well known in theart may then be applied to the insert to assist in the visual evaluationof the grinding finish and check for grinding cracks. The die penetrantis preferably removed by ultrasonic cleaning for approximately one hourin a soap and warm water mixture of about 56 degrees centigrade. Theinsert is then baked in an air fired oven of a type typically used indrying operations to thoroughly evaporate the cleaning mixture. It willbe appreciated that the use of the die penetrant and the cleaningprocedure used to remove the die penetrant from the insert may beomitted and has no effect on the present invention.

Applicants have found that, by initially thoroughly cleaning thesubstrate surface under vacuum by heating and ion etching the substratefor a sufficient length of time to present a surface free ofcontaminants and then depositing a first layer of titanium on thenonconductive substrate, the aforementioned problems associated withelectrical conductivity are overcome.

A ceramic substrate is placed within a chamber, evacuated and thenfilled with an inert gas, such as argon. The inert gas is partiallyionized and excited in the plasma as previously described. The ceramicsubstrate is then cleaned by heating and ion-etching. The ceramicsubstrate may be heated by any suitable means known in the art, such aselectron bombardment. In electron bombardment, a positive potential isplaced on the substrate within the chamber to attract electrons from thegaseous plasma. Under a vacuum of approximately 10⁻³ torr, the substrateis heated by the electrons striking the substrate surface therebyremoving various oxides from the substrate surface. The Si-Al-ON basedsubstrate and the Al₂ O₃ based substrate are preferably heated to atemperature of approximately 400° C. It should be noted that althoughthere is also a charge buildup during electron bombardment, the electroncurrent density between the substrate and plasma is high enough toovercome this buildup and thus allow surface heating by electronbombardment. The substrate is then subjected to ion-etching wherein thepolarity of the substrate is reversed to a negative potential to attractheavy argon ions typically used for ion-etching from the gaseous plasmato the substrate to further remove surface contaminants such as grease,dust and the like. Applicants have found, depending upon temperature,surface area of the insert to be cleaned, and degree of contamination, aceramic substrate may be cleaned in a vacuum after a period ranging fromapproximately four hours to six hours. For example, the higher theheating temperature the shorter the period of cleaning required toachieve a substrate substantially free of contaminants.

A first layer of titanium is then evaporated and deposited over thecleaned ceramic substrate. The titanium is evaporated and deposited forapproximately ten minutes by any known suitable means such as resistanceheating, electron bombardment, or radio-frequency inductive heating. Thedeposited titanium layer increases the electrical conductivity of theceramic substrate surface at the deposition temperature such thatelectrical biasing during the physical vapor deposition process becomeseffective.

A second layer of titanium nitride is then deposited upon the firstlayer. The second layer of titanium nitride is deposited by introducingnitrogen gas into the vacuum chamber to react with the titanium presentto form titanium nitride. The negative bias of the titanium coatedsubstrate causes a resultant glow discharge to increase the kineticenergy of the depositing titanium nitride material thereby resulting inthe deposition of a coating of titanium nitride of variable thickness.As a result of the present invention, excellent coating adhesion anddense coating structures may be obtained for a ceramic substrate.

The invention will be further clarified by a consideration of thefollowing examples. Several indexable metal cutting inserts inKennametal Si-Al-ON grades and Kennametal Al₂ O₃ grades of both Kenlocand Kendex styles as shown in FIG. 1 and FIG. 2, respectively; werecoated with titanium nitride. As shown in FIGS. 1 and 2 each metalcutting insert 10 has a flank face 12, a rake face 14 and a cutting edge16 at the juncture of the flank face and the rake face. Passing throughthe rake face of the Kenloc style insert shown in FIG. 1 is an opening18. Kenloc and Kendex are registered trademarks of Kennametal Inc. forcutting tools having an indexable cutting insert and for carbide cuttingtools, respectively.

The ceramic substrates were coated in a Balzers BAI 830 physical vapordeposition system having a vertically movable crucible. The ceramicsubstrates were heated under a vacuum of approximately 10⁻³ torr for aperiod ranging from approximately three hours to six hours. Titanium wasthen deposited on the cleaned ceramic substrates. Titanium nitride wasthen deposited on the titanium coating. Next, titanium nitride coatingthickness and adhesion were evaluated on the flank faces of the inserts.The coating thickness and degree of adhesion using the present inventionwere similar to that found in physical vapor deposition titanium nitridecoated cemented carbide substrates.

EXAMPLE 1

Several ceramic metal cutting inserts, styles SNGA-433 composed of Kyon2000 and Kyon 3000 were individually heated in separate test runs forapproximately 4 hours to a temperature of approximately 400° C. followedby 1/2 hour of ion etching at a pressure of approximately 10⁻³ torr in aBalzers BAI 830 system. An initial layer of titanium was then coated tothe insert surface by applying an arc current of approximately 125 ampsfor a period of approximately five minutes to the titanium within thecrucible as the crucible moved vertically within the vacuum chamber andthen increasing and maintaining the arc current to approximately 200amps for approximately five minutes. Nitrogen gas was then introducedinto the system for about 80 minutes to form a titanium nitride coatingon the insert surface.

Although the thickness of the titanium layer was too thin for opticalmicroscopic measurement, the presence of the titanium layer was observedby a transmission electron microscope. The titanium nitride coatingthickness was determined by the ball wear scar thickness test as setforth in Proc.9th Int. Conf. on CVD, Electrochemical Society,Pennington, N.J., 1984, P. K. Mehrotra, D. T. Quinto and G. J. Wolfe, P.757, which is incorporated herein by reference. The titanium nitridecoating thickness was measured to be approximately 2-3 micrometers onthe flank faces. The adhesion level of the coating was determined by theindentation test as set forth in Thin Solid Films, 154 (1987) 361-375which is also incorporated herein by reference. The coating thicknessand degree of adhesion using the present invention were similar to thatfound in physical vapor deposition titanium nitride coated cementedcarbide substrates. The adhesion level was determined to be greater thanor equal to 60 kg. on each sample tested.

EXAMPLE 2

Several ceramic metal cutting inserts, styles SNGA-433, composed of Kyon2000 and Kyon 3000 were individually heated in separate test runs forapproximately three hours to a temperature of approximately 400° C.followed by one-half hour of ion etching at a pressure of approximately10⁻³ torr in a Balzers BAI 830 system. An initial layer of titanium wasthen coated to the insert surface by applying an arc current ofapproximately 125 amps for a period of approximately five minutes to thetitanium within the crucible as the crucible moved vertically within thevacuum chamber. Arc current was then raised to approximately 200 Ampsand immediately nitrogen gas was then introduced into the system forabout 85 minutes to form a titanium nitride coating on the insertsurface.

The titanium nitride coating thickness was determined by the ball wearscar thickness test as set forth in Proc. 9th Int. Conf. on CVD,Electrochemical Society, Pennington, N.J., 1984, P. K. Mehrotra, D. T.Quinto and G. J. Wolfe, P. 757, which is incorporated herein byreference. The titanium nitride coating thickness was measured to beapproximately 2-3 micrometers on the flank faces. The adhesion level ofthe coating was determined by the indentation test as set forth inExample 1. The adhesion was inconsistent with some flaking of thecoating. The adhesion level was determined to be approximately less thanor equal to 30 kg due to insufficiently removed surface contaminants asa result of a shorter heating cycle as well as insufficient titaniumlayer coverage. It is believed that surface contaminants affected theapplication of the titanium layer to the substrate surface and in turnthe applied electrical biasing of the ion plating process.

EXAMPLE 3

Several ceramic metal cutting inserts, styles SNGA-433, composed of Kyon2000 and Kyon 3000 were individually heated in separate test runs forapproximately four hours to a temperature of approximately 400° C.followed by one-half hour of ion etching at a pressure of approximately10⁻³ torr in a Balzers BAI 830 system. An initial layer of titanium wasthen coated to the insert surface by applying to the titanium within thecrucible as the crucible moved vertically within the vacuum chamber anarc current increasing from approximately 125 amps to 200 amps over aperiod of approximately two minutes and then maintained at 200 amps forapproximately eight minutes. Nitrogen gas was then introduced into thesystem for about 80 minutes to form a titanium nitride coating on theinsert surface.

The titanium nitride coating thickness was determined by the ball wearscar thickness test as set forth in Proc. 9th Int. Conf. on CVD,Electrochemical Society, Pennington, N.J., 1984, P. K. Mehrotra, D. T.Quinto and G. J. Wolfe, P. 757, which is incorporated herein byreference. The adhesion level of the coating was determined by theindentation test as set forth in Example 1. The adhesion level wasdetermined to be greater than or equal to 60 kg.

It will be appreciated that the improved adhesive coating including afirst layer of titanium and second layer of titanium nitride adherentlydeposited to a ceramic substrate such as a cutting insert has been foundto reduce flank wear, and reduce the coefficient of friction between thecutting insert and a ferrous workpiece material. Moreover, becausetitanium nitride is chemically stable, titanium nitride has been foundto act as a diffusion barrier between the cutting insert and ferrous andnickel-based workpiece materials thereby reducing tool wear problems aspreviously described.

EXAMPLE 4

Several ceramic metal cutting inserts, styles TNG 332T composed ofapproximately 73 v/o Al₂ O₃ and 27 v/o TiC and known under thedesignation K090 as obtained from Kennametal Inc. were individuallyheated in separate test runs for approximately four hours to atemperature of approximately 400° C. followed by one-half hour of ionetching at a pressure of approximately 10⁻³ torr in a Balzers BAI 830system. An initial layer of titanium was then coated to the insertsurface by applying an arc current of approximately 125 amps over aperiod of approximately five minutes to the titanium within the crucibleas the crucible moved vertically upward within the vacuum chamber andthen applying an arc current of approximately 200 amps for approximatelyfive minutes as the crucible moved vertically downward within the vacuumchamber. Nitrogen gas was then introduced into the system for about 80minutes to form a titanium nitride coating on the insert surface.

Although the thickness of the titanium layer was too thin for opticalmicroscopic measurement, the presence of the titanium layer was observedby a transmission electron microscope. The titanium nitride coatingthickness was determined by the ball wear scar thickness test as setforth in Proc. 9th Int. Conf. on CVD, Electrochemical Society,Pennington, N.J., 1984, P. K. Mehrotra, D. T. Quinto and G. J. Wolfe, P.757, which is incorporated herein by reference. The titanium nitridecoating thickness was measured to be approximately 3 micrometers on theflank faces. The adhesion level of the coating was determined by theindentation test as set forth in Thin Solid Films, 154 (1987) 361-375which is also incorporated herein by reference. The coating thicknessand degree of adhesion using the present invention were similar to thatfound in physical vapor deposition titanium nitride coated cementedcarbide substrates. The adhesion level was determined to be greater thanor equal to 45 kg. on each sample tested.

EXAMPLE 5

Several ceramic metal cutting inserts, styles SNGA-433, havingapproximately 2.5 v/o SiC_(w), 10 v/o zirconia, 0.5 v/o magnesia and theremainder Al₂ O₃ as produced in accordance with U.S. Pat. No. 4,959,331;were ground to a fine surface finish, visually evaluated by the use of adie penetrant, and the ultrasonically cleaned as previously described.The inserts were then individually heated in separate test runs forapproximately four hours to a temperature of approximately 400° C.followed by one-half hour of ion etching at a pressure of approximately10⁻³ torr in a Balzers BAI 830 system. An initial layer of titanium wasthen coated to the insert surface by applying an arc current ofapproximately 125 amps over a period of approximately five minutes tothe titanium within the crucible as the crucible moved vertically upwardwithin the vacuum chamber and then applying an arc current ofapproximately 200 Amps for approximately five minutes as the cruciblemoved vertically downward within the vacuum chamber. Nitrogen gas wasthen introduced into the system for about 80 minutes to form a titaniumnitride coating on the insert surface.

The titanium nitride coating thickness was determined by the ball wearscar thickness test as set fourth in Proc. 9th Int. Conf. on CVD,Electrochemical Society, Pennington, N.J., 1984, P. K. Mehrotra, D. T.Quinto and G. J. Wolfe, P. 757, which is incorporated herein byreference. The titanium nitride coating thickness was measured to beapproximately 2.6 micrometers on the flank faces. The adhesion level ofthe coating was determined by the indentation test as set forth inExample 1. The adhesion level was determined to be greater than or equalto 45 kg. on each sample tested.

EXAMPLE 6

Several ceramic metal cutting inserts, styles SNGA-433, havingapproximately 5.0 v/o SiC_(w), 10 v/o zirconia, 0.5 v/o magnesia and theremainder Al₂ O₃ as produced in accordance with U.S. Pat. No. 4,959,331;were ground to a fine surface finish, visually evaluated by the use of adie penetrant, and the ultrasonically cleaned as previously described.The inserts were then individually heated in separate test runs forapproximately four hours to a temperature of approximately 400° C.followed by one-half hour of ion etching at a pressure of approximately10⁻³ torr in a Balzers BAI 830 system. An initial layer of titanium wasthen coated to the insert surface by applying an arc current ofapproximately 125 amps over a period of approximately five minutes tothe titanium within the crucible as the crucible moved vertically upwardwithin the vacuum chamber and then applying an arc current ofapproximately 200 Amps for approximately five minutes as the cruciblemoved moved vertically downward within the vacuum chamber. Nitrogen gaswas then introduced into the system for about 90 minutes to form atitanium nitride coating on the insert surface.

The titanium nitride coating thickness was determined by the ball wearscar thickness test as set forth in Proc. 9th Int. Conf. on CVD,Electrochemical Society, Pennington, N.J., 1984, P. K. Mehrotra, D. T.Quinto and G. J. Wolfe, P. 757, which is incorporated herein byreference. The titanium nitride coating thickness was measured to beapproximately 2.6 micrometers on the flank faces. The adhesion level ofthe coating was determined by the indentation test as set forth inExample 1. The adhesion level was determined to be greater than or equalto 45 kg. on each sample tested.

EXAMPLE 7

Several ceramic metal cutting inserts, styles SNGA-433, havingapproximately 1.5 v/o SiC_(w), 10 v/o zirconia, 0.5 v/o magnesia and theremainder Al₂ O₃ as produced in accordance with U.S. Pat. No. 4,959,331;were ground to a fine surface finish, visually evaluated by the use of adie penetrant, and then ultrasonically cleaned as previously described.The inserts were then individually heated in separate test runs forapproximately four hours to a temperature of approximately 400° C.followed by one-half hour of ion etching at a pressure of approximately10⁻³ torr in a Balzers BAI 830 system. An initial layer of titanium wasthen coated to the insert surface by applying an arc current ofapproximately 125 amps over a period of approximately five minutes tothe titanium within the crucible as the crucible moved vertically upwardwithin the vacuum chamber and then applying an arc current ofapproximately 200 Amps for approximately five minutes as the cruciblemoved moved vertically downward within the vacuum chamber. Nitrogen gaswas then introduced into the system for about 90 minutes to form atitanium nitride coating on the insert surface.

The titanium nitride coating thickness was determined by the ball wearscar thickness test as set forth in Proc. 9th Int. Conf. on CVD,Electrochemical Society, Pennington, N.J., 1984, P. K. Mehrotra, D. T.Quinto and G. J. Wolfe, P. 757, which is incorporated herein byreference. The titanium nitride coating thickness was measured to beapproximately 2.6 micrometers on the flank faces. The adhesion level ofthe coating was determined by the indentation test as set forth inExample 1. The adhesion level was determined to be greater than or equalto 45 kg. on each sample tested.

It will be appreciated that the improved adhesive coating including afirst layer of titanium and second layer of titanium nitride adherentlydeposited to a ceramic substrate such as a cutting insert has been foundto reduce flank wear, and reduce the coefficient of friction between thecutting insert and a ferrous workpiece material. Moreover, becausetitanium nitride is chemically stable, titanium nitride has been foundto act as a diffusion barrier between the cutting insert and ferrous andnickel-based workpiece materials thereby reducing tool wear problems aspreviously described.

The patents and patent applications referred to herein are herebyincorporated by reference.

Having described presently preferred embodiments of the invention, it isto be understood that it may be otherwise embodied within the scope ofthe appended claims.

What is claimed is:
 1. A tool insert coated by physical vapor depositionusing an applied electrical bias comprising:(a) a nonconductive ceramicsubstrate; (b) a first layer of titanium deposited by physical vapordeposition on said ceramic substrate; (c) a second layer of titaniumnitride adherently deposited on said first layer by physical vapordeposition; and (d) wherein said tool insert is a metal cutting inserthaving a flank face, a rake face and a cutting edge at the juncture ofsaid flank face and said rake face.
 2. The tool insert as set forth inclaim 1 wherein said titanium nitride layer is at least 2 micrometersthick.
 3. The tool insert as set forth in claim 1 wherein the adhesionlevel of said titanium nitride layer to said ceramic substrate surfacesis at least 60 kg in the indentation adhesion test.
 4. The tool insertas set forth in claim 1 wherein said ceramic substrate is an Al₂ O₃based ceramic.
 5. The tool insert as set forth in claim 1 wherein saidceramic substrate is an Al₂ O₃ based ceramic having SiC whiskersdispersed therein.
 6. The tool insert as set forth in claim 1 whereinsaid ceramic substrate is an Al₂ O₃ based ceramic having ZrO₂ dispersedtherein.
 7. The tool insert as set forth in claim 1 wherein said ceramicsubstrate is an Al₂ O₃ based ceramic having TiC dispersed therein. 8.The tool insert as set forth in claim 1 wherein said ceramic substrateis an Al₂ O₃ -based ceramic having SiC whiskers and ZrO₂ dispersedtherein.
 9. The tool insert as set forth in claim 1 wherein said ceramicsubstrate is an Al₂ O₃ -based ceramic having TiC whiskers dispersedtherein.
 10. The tool insert as set forth in claim 1 wherein saidceramic substrate is an Al₂ O₃ -based ceramic including magnesia and SiCwhiskers and ZrO₂ dispersed therein.
 11. The tool insert as set forth inclaim 1 wherein said ceramic substrate is selected from the groupconsisting of silicon nitrides and sialons.
 12. The tool insert as setforth in claim 1 wherein said ceramic substrate consists essentially ofbeta-prime sialon and a glassy phase.
 13. The tool insert as set forthin claim 1 wherein said ceramic substrate consists essentially ofalpha-prime sialon, beta-prime sialon and a glassy phase.